1. Field
Example embodiments relates to methods of manufacturing a thin film transistor. Other example embodiments relate to methods of manufacturing a thin film transistor including an oxide semiconductor as a channel material.
2. Description of the Related Art
Because an oxide semiconductor may have a substantially high carrier density, a thin film transistor having the oxide semiconductor is usually operated in a depletion mode (i.e., a state where a substantially high current flows at a gate voltage of 0 V). As such, in order to turn off an oxide semiconductor thin film transistor, a larger negative gate voltage may be needed. In order to realize a display device having lower power consumption, a threshold voltage approaching a positive value may be desirable.
The oxide semiconductor may have a substantially high carrier density due to an oxygen deficiency in the oxide semiconductor, which leads to an excessive supply of carriers. As such, the electrical characteristics of the oxide semiconductor may be easily changed (or influenced) by external factors (e.g., plasma damage and water or oxygen absorbed in the oxide semiconductor). In order to realize a more stable and more reliable oxide semiconductor thin film transistor, a passivation layer that blocks external factors may be desirable.
A silicon oxide layer may be used as a passivation layer in a conventional oxide semiconductor because oxygen supplied from deposition of the silicon oxide layer suppresses the generation of excessive carriers in an oxide semiconductor. As such, the threshold voltage of the thin film transistor may be maintained within a desirable range.
A silicon oxide layer, opposed to a silicon nitride layer, may be desirable as a passivation layer against external factors (e.g., water or oxygen). A silicon nitride layer may have more functionality as a passivation layer, but does not contain oxidative ions. A substantially high leakage current may be generated by deoxidation of the oxide semiconductor due to a substantially large amount of hydrogen.